The present invention is related to a protein isolated from the cell wall of the bacterium Pseudomonas maltophilia and having the ability to bind IgA immunoglobulins, as well as IgG immunoglobulins, said protein having a molecular weight of approximately 30,000 daltons. The present invention is further related to the use of said protein in the isolation and purification of IgA immunoglobulins, and the isolation and purification of bacteria having specific desired characteristics.
2. Technical Background
In the art a number of immunoglobulin binding proteins are known and widely used. In particular, a number of such proteins are known which are capable of binding the Fc region of IgG immunoglobulins. For example, various strains of Staphylococcus aureus carry a Type I receptor, commonly known as Protein A. Protein A is known to bind the Fc region of IgG. As would be expected, the ability of Protein A to bind IgG at its Fc region has made it an important immunological tool. For example, the binding characteristics of Protein A allow it to be employed in separating IgG immunoglobulins from other materials, and in diagnosing conditions involving abnormal levels of IgG immunoglobulins.
Other materials are also known to have immunoglobulin binding properties. Certain strains of Groups A, C, and G of streptococci possess a Type II receptor on their surface which also binds the Fc region of IgG. A receptor on Groups C and G Streptococci has been reported which binds the F(ab.sup.1).sub.2 region of IgG. Thus, it can be seen that a number of immunoglobulin binding proteins have been identified and used.
In addition to the conventional immunoglobulin binding proteins mentioned above, the existence of binding proteins which bind to regions outside the Fc region have also been reported, and are now known in the art. There exist, for example, bacterial cell-wall proteins which bind large fractions of polyclonal IgM, with affinity for IgG light chains, as well as binding of kappa and lambda light chains to Group A Streptococci. Thus, workers in the art continue to identify, substances which bind one or more immunoglobulins at a specific region.
One problem that has been encountered is the lack of satisfactory immunoglobulin binding proteins which are capable of specifically binding IgA immunoglobulins. While some IgA binding materials have now been reported, the effectiveness of these materials in actual laboratory and clinical practice has been limited. At the same time, binding materials which are typically useable in the laboratory or clinic have not bound IgA. For example, the widely used and accepted Proteins A and G bind IgG immunoglobulins but are not known to bind IgA.
The lack of suitable IgA binding materials renders difficult the production of pure IgA immunoglobulins. Without an acceptable IgA binding protein it is not practical to produce IgA from a mixture of biological fluids. IgA is instead produced from a myeloma cell line (available from the American Type Culture Collection, Rockville, Md.) which produces murine monoclonal IgA antibody to trinitrophenol.
The IgA produced from this cell line then requires further processing and purification to remove impurities. This process is complex and expensive and requires additional purification procedures prior to use of the collected product. One of the results of these problems is that IgA immunoglobulins are scarce and their use in research and in medicine is correspondingly limited. The production of pure IgA is also extremely expensive, requiring the steps of producing the monoclonal product and the additional purification steps.
The lack of readily available IgA binding proteins has made it difficult to conduct studies of the presence, characteristics, and effects of IgA immunoglobulins. For example, certain diseases are known to be accompanied by abnormal levels of IgA immunoglobulins. Such diseases include IgA-related myeloma, certain gastrointestinal diseases, and some kidney diseases. It would be helpful to be able to easily and readily quantify IgA in order to aid in diagnosis of these abnormalities. With present purification techniques for IgA, however, such diagnosis is necessarily limited in scope.
It would certainly be of interest to further study the causes of the diseases mentioned above, but the limited availability of IgA and IgA binding materials limits this work. It would also be of interest for research and diagnostic purposes to isolate IgA containing bacteria and to separate those bacteria from other bacteria. Clearly, an effective and useable IgA binding material would facilitate this procedure.
Accordingly, it would be an advancement in the art to provide a material which readily bound IgA immunoglobulins. It would be another advantage to provide such a material which could be readily and easily used in the purification of IgA, thus avoiding the complex and expensive IgA isolation procedures presently in use.
It would be a related advancement in the art to provide a simple and easily operable method for isolating IgA immunoglobulins from a wide variety of biological fluids. It would also be an advancement in the art to provide a mechanism for separating bacteria containing IgA immunoglobulins from bacteria lacking IgA immunoglobulins. It would be a further advancement in the art to provide diagnostic and research means for quantifying IgA in disease mechanisms and in studying IgA-related illnesses.
The such methods and compositions are disclosed and claimed herein.